Dynamic Contact Angle Reformulates Pore-Scale Fluid-Fluid Displacement at Ultralow Interfacial Tension

Abstract

SummarySurfactant flooding is an effective enhanced oil recovery method in which the oil/water interfacial tension (IFT) is reduced to ultralow values (<0.01 mN/m). The microscopic fluid-fluid displacement has been extensively studied at high IFT (>10 mN/m). However, the microscopic displacement dynamics can be significantly different when the IFT is ultralow because the dynamic contact angle increases with the increase of the capillary number. In this study, surfactant flooding was performed and visualized in micromodels to investigate the dynamics of multiphase displacement at ultralow IFT. Although the micromodels used were strongly water-wet, the displacements of oil by surfactant solutions at ultralow IFT appeared as drainage. Furthermore, a macroscopic oil film was left behind on the surface, which indicates that a contact line instability occurred during displacements. The shape of the oil/water meniscus was determined by the balance between viscous forces and capillary forces. The meniscus can be significantly distorted by viscous forces at ultralow IFT. Therefore, the water-wet micromodel exhibits an oil-wet behavior at ultralow IFT, and the displacements of oil by surfactant solutions at ultralow IFT manifested as drainage rather than imbibition. The flow behavior is further complicated by the spontaneous formation of microemulsion during displacement. The microemulsion is mainly formed from the residual oil. The formation of a microemulsion bank made the surfactant solution discontinuous, with transport in the form of droplets in the microemulsion bank and displacement front. The novelty of this work is to reveal the effects of dynamic contact angle on the ultralow IFT displacement.

Micromodel Studies of Surfactant Flooding for Enhanced Oil Recovery: A Review

“…Copyright 2017 American Chemical Society]. (c) Significant increase of apparent contact angle during ultralow IFT surfactant flooding in water-wet micromodels [Reprinted with permission from ref . Copyright 2020 Society of Petroleum Engineers].…”

“…For low IFT surfactant flooding in water-wet reservoirs, the capillary number is not high enough to significantly increase the advancing contact angle so that the oil remains the nonwetting phase, thus forming O/W emulsions (Figure a). For ultralow IFT surfactant flooding in water-wet reservoirs, the large capillary number makes the advancing contact angle greater than 90° (Figure c), resulting in the formation of W/O emulsions rather than O/W emulsions during the displacement (Figure d). , The formation of viscous W/O emulsion during ultralow IFT surfactant flooding increases the pressure gradient and sweep efficiency, which effectively improve the heavy oil recovery.…”

Abnormal Phenomena and Mathematical Model of Fluid Imbibition in a Capillary Tube

“…Soares et al (2005) [16] found that an uncertainty of contact angle in imbibition studies since the displaced liquid can stick to the capillary-tube wall and consequently influences contact angle during this imbibition process. The uncertainty of contact angle on process of imbibition is also related to interfacial tension [17,18]. Thus, the contact angle (which is influenced by the above factors) is likely to affect imbibition rate, but it does not affect the law of imbibition rate with time.…”

Effect of Surfactant‐Assisted Wettability Alteration on Immiscible Displacement: A Microfluidic Study

“…However, in‐situ wettability alteration induced by surfactants cannot be captured using this method. The emergence of microfluidics has made it possible to visualize and investigate the fluid‐fluid displacement at the pore‐scale (Günther & Jensen, 2006; Stone et al., 2004; Yang, Lu, et al., 2021). Using microfluidics, Zhong et al.…”